REPORT ON THE RADIOLARIA. 475 



Subgenus 2. Hymenactinium, Haeckel. 

 Definition. Distal ends of the arms armed with terminal spines. 



5. Hymenactura ptolemcei, n. sp. 



Astromma sp., Bury, 1862, Polycystins of Barbados, pi. xv. figs. 5, 6. 



Phacoid shell twice as broad as the medullary shell, with six to seven pores on its radius. 

 Arms nearly square, about as large as the phacoid shell, at the truncated distal end little broader 

 than at the base, and armed with a strong pyramidal terminal spine. Patagium incomplete, 

 enveloping the basal half of the arms. 



Dimensions. Diameter of the phacoid shell 01, of the medullary shell 0'05 ; length and 

 greatest breadth of the arms 0'08. 



Habitat. Pacific, central area, Station 268, depth 2900 fathoms ;. fossil in the rocks of Barbados. 



6. Hymenactura copernici, n. sp. (PI. 38, fig. 9). 



Phacoid shell three times as broad as the medullary shell, with six pores on its radius. 

 Arms lanceolate, nearly twice as long as the phacoid shell, in the middle part twice as broad as 

 the medullary shell, with a strong conical terminal spine at the distal end. In each arm about 

 ten transverse rows of chambers. Patagium enveloping the basal half of the arms, with four convex 

 parallel rows of chambers. 



Dimensions. Diameter of the phacoid shell 01, of the medullary shell 0'035 ; length of the 

 arms 017, greatest breadth 0'07. 



Habitat. Pacific, central area, Station 266, depth 2750 fathoms. 



Genus 208. Astractura, 1 Haeckel, 1881, Prodromus, p. 459. 



Definition. C occodiscida with four chambered arms on the margin of the 

 circular or quadrangular disk, crossed in two equatorial diameters, without a connecting 

 patagium. 



The genus Astractura has the form of a regular cross, four radial arms being 

 opposite in two equatorial diameters perpendicular one to another. In the Porodiscida 

 the same form is repeated by Stauralastrum, in the Spongodiscida by Spongasteriscus. 

 The oldest known species of the genus is Astromma aristotelis of Ehrenberg, in which 

 genus this author confounded triradial and four-radial forms. 



1 Astractura = Star-shaped shell with many rays ; owrgoi/, dwis, ou^x. 



